Masato is a professional Japanese Welterweight kickboxer and a two-time K-1 World MAX champion. He won his first K-1 World MAX title on July 5, 2003 by defeating Mike Zambidis in the quarterfinals, knocking out Sakkedaw Kiatputon in the semifinals and defending champion Albert Kraus with a left hook KO in the tournament finals. Masato was also the K-1 World MAX tournament finalist in 2004 and 2007. On October 1, 2008 Masato won his second K-1 MAX title, defeating Yoshihiro Sato and Artur Kyshenko.

Masato Kobayashi (小林 雅人) was born in Chiba, Japan on March 10, 1979. He started training kickboxing at the age of 17 and made his professional debut on March 23, 1997 against Hutoshi Takehara. Masato won his professional debut by KO in the first round. After three years of fighting for the All Japan Kickboxing Federation, Masato fought some fights in Thailand, Wolf Revolution and K-1. Since 2002, after K-1 introduced their middlweight (70kg/154lb) division, Masato has been one of their most popular and dominant fighters. He is the only K-1 World MAX champion that has yet to be knocked unconscious in a professional match and is also the only fighter that has qualified for the semi-finals of every single K-1 World MAX tournament (2002-2008). Masato has appeared in films such as Izo, Buyuden, Dead or Alive 2, Shukyoku Ninja and Shamo. He is the husband of Japanese actress Shin Yazawa.

Masato started fighting for the All Japan Kickboxing Federation when he was 18 years old. He stayed there for three years and became the welterweight champion at the age of 20 by knocking out Tomoharu Chiba on March 17, 1999. He only lost one fight in the AJKF to Takayuki Kohiruimaki.

Much of Masato's early career was spent training in Thailand, although he only fought there twice. In his first match in Thailand, Masato knocked Kongnapa Looktubpha out cold with a swift left uppercut. Later that year he was scheduled to fight Orono Por.Muang U-Bon but due to speculation that Orono had hepatitis, Masato's team opted not to fight, only days before the event. Instead, he fought Suriya Sor.Pleonchit, a highly ranked southpaw, who would later go on to compete in the 2004 Summer Olympics and win a bronze medal in Welterweight boxing. Masato was unprepared for Suriya's southpaw style and was dominated for the entire five rounds.

Wolf Revolution was an event that mixed live bands with MMA and kickboxing matches. Masato headlined on each event and won all of his fights by KO. Masato's last fight for the Wolf Revolution was against Canadian Melvin Murray, who he managed to finish in the 2nd round. Masato fought two more semi-contact exhibition matches for the Wolf Revolution, including a single round of MMA rules against Caol Uno.